We have measured the thermal variation of the magnetoresistance of several series of soft spin-valve structures TMl/NM/TM2/antiferromagnet between 77 K and 350 K. TM1 and TM2 are ferromagnetic transition metals or their alloys (Co, Ni, Ni8oFe2o), the magnetization of TM2 is constrained by exchange coupling to an antiferromagnet, NM is Cu or Au. We show that the amplitude of the spin-valve effect (magnetoresistance AR/R due to the change in relative orientation of the magnetizations of adjacent ferromagnetic layers) decreases almost linearly with temperature. An exponential decrease of the spin-valve amplitude is found vs. the thickness of the noble-metal interlayer with a characteristic decay length nearly independent of temperature. Consequently, we demonstrate that the thermal decrease of the magnetoresistance of these structures is not due to increased scattering in the noble-metal spacer, but mainly to spin j" and spin v intermixing in the ferromagnetic layers. © 1991 IOP Publishing Ltd.